1. Field of the Invention
The present invention relates to medical equipment technology and more particularly, to a fluid withdrawing, expelling and filtering apparatus for sampling specimens from a fluid.
2. Description of the Related Art
U.S. Pat. No. 5,494,044 teaches a sampling device with a one-way valve including a cell filter for taking a sample of amniotic fluid. However, the filter provides no guide means, and a large amount of the cells in the intake flow of the amniotic fluid can be lost, resulting in an adequate amount of sampled cells.
U.S. Pat. No. 6,796,965 discloses a syringe with filter that has guide means mounted in the central axis and a filter element located on the circumference, thus, its reciprocating displacement in unstable and can be biased easily. Further, mounting the filter element in the circumference can cause formation of mixed flow, leading to a poor filtration effect.
Therefore, the prior art sampling devices are still not satisfactory in function, and have still room for improvement.